The present invention relates to a rail fastening device and, more particularly, to a rail fastening device suitable for use in a wooden sleeper section of railroad construction for trains of a motive power having a heavy axle load and freight cars of heavy weights.
A typical conventional rail fastening device which has been used for wooden sleeper section of railroad construction will be explained hereinunder with specific reference to FIGS. 1 and 2. A tie plate 2 is fastened by dog spikes 3 on the upper surface of a sleeper 1. A rail 4 is mounted on the central portion of the tie plate 2. As will be seen from FIG. 2, the tie plate 2 is provided at its both sides with notches 5 to which bolts 6 are fastened at their lower ends. The notches 5 receive also the base ends 8 of leaf springs 7. The leaf spring 7 is bent at about 180.degree. at its intermediate bent portion 9, and a bolt hole 11 is formed in the portion of the leaf spring 7 between the end 10 and the bent portion 9. For inserting the base end 8 of the leaf spring 7 into the notch 5 of the tie plate 2, the bolt 6 is inserted into the bolt hole 11 and a nut 12 is screwed to the bolt 6 from the upper end thereof. As the nut 12 is tightened, the end 10 of the leaf spring 7 is brought into pressure contact with the rail 4 thereby to resiliently fasten the rail 4 to the tie plate 2.
This conventional rail fastening device, however, showed the following disadvantages when used in a railroad section under severe load condition.
(1) The hole 11 is formed in such a portion of the leaf spring 7 that undergoes the greatest stress, so that it is necessary to increase the thickness of the leaf spring 7 for attaining a higher safety. In consequence, the amount of material used is increased and, hence, the spring constant with respect to the end 10 is increased to make it difficult to follow up slight vibrations of the rail.
(2) The nut 12 is tightened with a force which is about 2 times as large as the force with which the end 10 of the leaf spring 7 fastens the rail 4. In consequence, the bolt 6 is deteriorated soon, namely the bolt 6 cannot have sufficient durability.
(3) The leaf spring 7 having the simple construction as shown in FIG. 2 cannot produce sufficient resistance to the turning of rail sideways which may be caused by an excessively large lateral force. It is possible to use a fastening spring having such a two-staged linear spring constant as having a large spring constant in order to bear upward load which tends to turn the rail sideways but a small spring constant for tightening fixedly the rail. Such a spring, however, has an impractically complicated construction and is difficult to fabricate. In addition, such a spring cannot sufficiently receive surface treatment required to attain sufficient durability. Thus, it takes much money for putting such a spring into practical use.
(4) The lateral force generated during running of the train is finally received by the dog spikes 3. However, when the lateral force is extremely large, the durability of the dog spike 3 is deteriorated and, at the same time, the sleeper 1 is damaged soon. In addition, frequent railroad maintenance work is required for preventing the dog spikes 3 from becoming loose.
It is advantageous that the rail fastening spring has a large thickness for producing a large resistance to the force which acts to turn the rail sideways. On the other hand, in order that the spring can exert its characteristics to follow up fine vibrations of the rail, it is necessary that the end of the leaf spring has as small a spring constant as possible.